At least some do although perhaps not in the way you are thinking. Old, but still new enough to be digitally distributed games could still bring in the occasional revenue. But games with physical aspects (cartridges) are eventually no longer manufactured and eventually their first-party sales revenue will dry up.
However, it may still be possible to make money on the licensing of the IP or sale of related property, and a company may account that as revenue from from products.
As for why “old” games aren’t always released for free, well, it tends tends to come down to the fact that the owner wants to maybe make money re-releasing the game in the future or that making it available for free would actually cost them (in manufacturing, hosting or support for example) and thus not be an attractive business proposition.